A golf ball typically includes an outer spherical surface with depressions or dimples on said outer surface. The portions of the outer surface between the dimples are commonly referred to as frets and form the un-dimpled surface of the golf ball. The dimples perturb the air flow surrounding the golf ball and create air turbulence as the ball moves through the air. Turbulence and aerodynamic drag are related by a complicated relationship. The dimples are intended to create the appropriate amount of turbulence to reduce the aerodynamic drag and optimize golf ball performance.
The aerodynamic design of golf balls has historically concentrated on the shape, size, and arrangement of the dimples. In general, little or no attention has been paid to the size and shape of the spaces or frets between the dimples. The natural tendency is to view the golf ball as a 1.68 inch diameter sphere with depressions on the surface.
However, the air flow over the surface does not have such a perceptual bias. The air flow “sees” only a textured surface and has no special regard for whether the texture is provided by a large sphere with depressions in the surface or a smaller sphere with projections on the surface. In fact, the contours of the raised areas between the dimples, i.e., the frets, may have a greater effect of air flow than the shape of the dimples.
If there is an optimal fret width, it is not being exploited on conventional golf balls with dimples having a circular periphery. Circular dimples have a maximal packing efficiency and the spaces between them are not necessarily constant. Further, the cross section of the frets between circular dimples is not rotationally symmetric but changes continuously.
Worst, U.S. Pat. No. 4,284,276, for a Grooved Golf Ball, discloses both grooves and dimples which are distinct surface texture members which have unique locations, however neither a groove nor a dimple is located on top of another member.
Examples of overlapping dimples exist in the prior art, but they are separate surface members of a single pattern or design whose individual members have expanded in size to create an intersection.
Numerous prior art golf balls and references include secondary surface texture features which appear within the primary surface feature. “Dimples within dimples” or various means of creating surface texture inside a spherical dimple or polygon are found. What is desired is to have the secondary surface feature appear predominantly outside the region defined as the primary surface feature, such that a surface texture is created where dimpling is not present.
Kennedy, U.S. Pat. No. 6,626,772, for a “Golf Ball With Elevated Dimple Portions”, describes a dimple having an elevated portion such as an annular ring and an edge on only the primary surface texture elements which appear elevated to the ball surface.
An example of using two or more techniques to create additional surface texture is described in Barfield, U.S. Pat. No. 6,547,678, wherein a combination is includes consisting of conventional smooth interior surface spherical dimples and unusually shaped dimples (which include textural elements within them).
The Callaway HX Series golf balls, such as described in U.S. Pat. No. 6,634,965, describe a tubular lattice which comprises the outer diameter of the ball. The surface consists of a well defined series of substantially interconnected line segments located between and defining geometric depressions. The tubular lattice structure replaces the conventional non-dimpled space between dimples. The highest elevations of ridges correspond to the inter-dimple space in a conventional dimple pattern, i.e. the frets. However, these areas do not contain a secondary surface texture as described in the present invention.
Another example of a golf ball having an unusual appearance derived from the proximal location of square and circular dimple types to create the appearance of a geometric protrusion outlining the spherical indentation of dimples is described in U.S. Pat. No. 5,106,096 which relates to a Bullet D.F.S. golf ball. The circular and square cross-section dimples are effectively distinct members of a single surface texture having an unusual inter-dimple geometry. The inter-dimple space does not include a secondary surface texture feature.
Accordingly, it is an object of the present invention, to create a secondary feature intended to appear predominantly in the fret areas of the golf ball surface. This will be a first machining operation prior to cutting the primary surface feature into the master tool, the “hob”, used to make the ball molding cavities.